Significance of Ni supply for growth, urease activity and the concentrations of urea, amino acids and mineral nutrients of urea-grown plants

The effect of Ni supply on growth, N metabolism and leaf urease activity of six plant species (rye, wheat, soybean, rape, zucchini and sunflower) grown on urea-based nutrient solutions was investigated. Activity of urease, which is activated by Ni, was hardly detectable in plants of all six species grown without supplementary Ni. As a consequence Ni-deprived plants accumulated considerable amounts of urea, showed a reduced dry matter production and reduced total N concentrations. The lack of urease activation in low-Ni plants made them metabolically N deficient, which is illustrated by the chlorotic appearance of these plants. The soluble amino acid N concentration was reduced by inadequate Ni supply. The amide concentrations (glutamine, asparagine) were considerably affected in all species. The same applied to the concentrations of the urea cycle intermediates arginine, ornithine, and citrulline. These results stress the necessity of Ni for urease activation and thus for the growth of plants on urea-based media.